Compilation for GTK+ using OpenGL - c++

Question

Context: I am learning development of GUI using GTK+. I also wanted to draw lines and circles on the GUI. So I started with the tutorials and I am stuck with the part of GtkGLArea. I am following the code given in the GTK+ documentation
The error:
glTrial.cpp:32:13: error: variable or field ‘on_realize’ declared void
on_realize (GtkGLarea *area)
^
glTrial.cpp:32:13: error: ‘GtkGLarea’ was not declared in this scope
glTrial.cpp:32:24: error: ‘area’ was not declared in this scope
on_realize (GtkGLarea *area)
I believe I am not compiling properly and the compiler is not able to find correct headers.
Compilation:
g++ -std=c++14 \`pkg-config --cflags gtk+-3.0\` -o glTrial glTrial.cpp \`pkg-config --libs gtk+-3.0\`
The code:
#include <gtk/gtk.h>
#include <gtkgl-2.0/gtkgl/gdkgl.h>
#include <gtkgl-2.0/gtkgl/gtkglarea.h>
static void
print_hello (GtkWidget *widget,
gpointer user_data)
{
g_print ("Hello World\n");
}
static gboolean
render (GtkGLArea *area, GdkGLContext *context)
{
// inside this function it's safe to use GL; the given
// #GdkGLContext has been made current to the drawable
// surface used by the #GtkGLArea and the viewport has
// already been set to be the size of the allocation
// we can start by clearing the buffer
//glClearColor (0, 0, 0, 0);
// glClear (GL_COLOR_BUFFER_BIT);
// draw your object
// draw_an_object ();
// we completed our drawing; the draw commands will be
// flushed at the end of the signal emission chain, and
// the buffers will be drawn on the window
return TRUE;
}
static void
on_realize (GtkGLarea *area)
{
// We need to make the context current if we want to
// call GL API
gtk_gl_area_make_current (area);
// If there were errors during the initialization or
// when trying to make the context current, this
// function will return a #GError for you to catch
if (gtk_gl_area_get_error (area) != NULL)
return;
// You can also use gtk_gl_area_set_error() in order
// to show eventual initialization errors on the
// GtkGLArea widget itself
GError *internal_error = NULL;
init_buffer_objects (&error);
if (error != NULL)
{
gtk_gl_area_set_error (area, error);
g_error_free (error);
return;
}
init_shaders (&error);
if (error != NULL)
{
gtk_gl_area_set_error (area, error);
g_error_free (error);
return;
}
}
static void
activate (GtkApplication* app,
gpointer user_data)
{
GtkWidget *window;
GtkWidget *grid;
GtkWidget *button;
GtkWidget *gl_area =gtk_gl_area_new();
/* Create a new window, and set its title */
window = gtk_application_window_new(app);
gtk_window_set_title(GTK_WINDOW(window), "Window");
gtk_container_set_border_width(GTK_CONTAINER(window), 10);
// gtk_window_set_default_size(GTK_WINDOW(window), 200, 200);
/* Here we construct the container that is going to pack the buttons*/
grid = gtk_grid_new();
/* Pack the container in the window */
gtk_container_add (GTK_CONTAINER (window), grid);
button = gtk_button_new_with_label ("Quit");
g_signal_connect_swapped (button, "clicked", G_CALLBACK (gtk_widget_destroy), window);
gtk_grid_attach (GTK_GRID (grid), button, 0, 0, 2, 1);
button = gtk_button_new_with_label ("Hello");
g_signal_connect_swapped (button, "clicked", G_CALLBACK (print_hello), NULL);
gtk_grid_attach (GTK_GRID (grid), button, 0, 1, 2, 1);
/* Trial for GL area*/
g_signal_connect (gl_area, "render", G_CALLBACK(render), NULL);
gtk_grid_attach (GTK_GRID (grid), gl_area, 0, 2, 10, 10);
gtk_widget_show_all (window);
}
int
main (int argc,
char **argv)
{
GtkApplication *app;
int status;
g_application_run (G_APPLICATION (app), argc, argv);
// app = gtk_application_new("org.gtk.example", G_APPLICATION_FLAGS_NONE);
g_signal_connect(app, "activate", G_CALLBACK (activate), NULL);
status = g_application_run (G_APPLICATION (app), argc, argv);
g_object_unref (app);
return status;
}

Answer 1

According to a fast google, you are looking for GtkGLArea, note the uppercase A.
– derhass

Answer 2

you need:
sudo apt install *epoxy*
and
c++ t.c --target=arm-linux-gnu `pkg-config --libs --cflags gtk+-3.0 epoxy ` -o op